Evaporative emission system

ABSTRACT

A fuel vapor recovery system for the adsorption, storage and eventual recycling of vapors to an engine. The system has a vapor-storage canister containing activated carbon for adsorbing fuel vapors from various parts of the engine fuel system. The system selectively purges the fuel vapors for introduction to the engine intake manifold. The purging is controlled in response to engine loading and engine speed for improved engine operation.

United States Patent 1191 Haase et al.

[451 Oct. 21, 1975 EVAPORATIVE EMISSION SYSTEM [75] Inventors: LawrenceH. Haase, Belleville;

David R. Liimatta, Livonia, both of Mich.

[731 Assignee: Ford Motor Company, Dearborn,

, Mich.

[22] Filed: Apr. 4, 1973 '21 Appl. No.: 347,959

[52] US. Cl 123/136; 123/121 [51] Int. Cl. F02M 25/08 [58] Field ofSearch 123/136, 121; 60/285, 301

[56] References Cited UNITED STATES PATENTS 3,352,294 11/1967 Biller etal. 123/136 3,674,423 7/1972 Klimisch 60/301 3,680,318 8/1972 Makajima60/290 Beveridge 123/136 Hollis, Jr 123/136 Primary Examiner-Charles J.Myhre Assistant ExaminerTony Argenbright Attorney, Agent, or Firm.losephW. Malleck; Keith L. Zerschling [57] ABSTRACT A fuel vapor recoverysystem for the adsorption, storage and eventual recycling of vapors toan engine. The system has a vapor-storage canister containing activatedcarbon for adsorbing fuel vapors from various parts of the engine fuelsystem. The system selectively purges the fuel vapors for introductionto the engine intake manifold. The purging is controlled in response toengine loading and engine speed for improved engine operation.

4 Claims, 1 Drawing Figure US. Patent Oct. 21, 1975 3,913,545

EVAPORATIVE EMISSION SYSTEM BACKGROUND OF THE, INVENTION In an effort toreduce hydrocarbonemissions from the fuel system, various evaporativeloss control devices have been proposed, which typically comprise acanister filled with suitable adsorbent material, such as activatedcharcoal. The carbon adsorbs the hydrocarbon vapors when the engine isnot in operation; when the engine is operative, means are provided toeffect desorption or purging of the vapors from the adsorbent materialso that these vapors can be fed to combustion chambers of the engine forconsumption therein. During engine operation, the running vapor lossesfrom both the fuel tank and carburetor bowl are being consumed as theyare generated. This approach has worked successfully to reducehydrocarbon emissions to the atmosphere, but under certain engineoperating conditions, the introduction of both the stored and currentlygenerated hydrocarbon vapors for consumption in the engine affectsengine operation or causes an increase in the exhaust emission ofunburned hydrocarbons. On other occasions, only the stored vapors maycause an over rich air/fuel mixture during the initial portion of thepurged cycle. The latter can result in such a rich mixture that engineperformance becomes irregular and poor (i.e., hesitation and stumbleaffecting drivability) and most importantly thecarbon monoxide contentof the exhaust is increased.

Although the prior vapor emission systems have been concerned with theneed for a controlled purge of hydrocarbon vapors to avoid some of theabove problems, the attempts have not been entirely successful. Forexample, there has been proposed a system which would have twoadsorption beds connected in series to each other. Upon purging, theseries connected adsorbent beds are unloaded sequentially therebyresulting in some degree of modulated release.

Another approach is the use of a canister bypass for providing avariable purge rate. The canister bypass attempts to smooth out theair/fuel ratio since the amount of air going ultimately through thethroat of the carburetor will be'constant, while the amount of air goingthrough the adsorbent material increases or de- 'creasesin the responseto the amount of air bypassing the adsorbent. In this manner, acontrolled amount of purged fuel vapors may be obtained to some degree.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide an improved apparatus and method for a fuel vapor recoverysystem; purging of the system is controlled so that overrichness isavoided in the mixturereceiving the recovered vapors and thereby avoidmomentary sag or poor engine performance.

Still another object of this invention is to provide a means ofcontrolling the return of excess fuel vapors to the combustion cycle ofthe engine in such a manner that the carburetor air-fuel ratio ismaintained at least above 14/1, thus avoiding a significant change inthe combustion products of the engine, such as carbon monoxide. Thisbecomes significant particularly with respect to total auto emissioncontrols which may employ a catalytic converter to reduce unwantedgaseous constituents of the exhaust; in many cases the catalyticconverter requires a controlled feed (within a limited range) of carbonmonoxide as part of the exhaust being introduced to the catalyticconverter.

SUMMARY OF THE DRAWING The FIGURE is a schematicillustration of variouscomponents comprising an evaporative emission control systemQThere isshown in cross-section a storage canister for fuel vapors as well asfirstand second purge control means and a typical carburetor usedwith aconventional internal combustion engine.

DETAILED DESCRIPTION Referring now to the drawing, there is illustrateda fuel vapor recovery system adapted for recovering fuel vapors whichmay collect in the carburetor fuel bowl or the vehicle fuel tank. Ingenerahthe recovery system comprises a canister A containing a bed ofadsorption material in the form of activated carbon, a passage Bcommunicating the interior of said canister with the intake manifold Cof an internal combustion engine D at a location downstream of throttle11. The recovery system further comprises a first control means Eemployed to completely shut off or completely open the passage B inresponse to a vacuum signal received from a location 9 upstream from thethrottle 11 of carburetor 12, but downstream from the venturirestriction 13 of the carburetor; this location is commonly referred toas the spark port. A second control means F is employed to operate inseries with said first control means and is effective to modulate theflow of fuel vapors through said passage in response to the magnitude ofthe vacuum received from location 10, thereby controlling the aperturethrough a portion of passage B.

The canister may typically comprise a container 14 having the bed ofadsorption material 15 substantially filling said container, except foran air space 16 defined by a screen 20 at the bottom thereof; a freshair intake 17 is arranged to admit air to said space 16 during a purgingphase of the system. Fuel vapors are conveyed to the canister at the topthereof by way of a conduit 18 leading from a vehicle fuel storage tankand a conduit 19 leading from the carburetor fuel bowl. Thus, duringinoperative conditions of the engine or hot soak cycles, fuel vapors arereleased and adsorbed by the adsorption bed 15, the passage B beingclosed thereby maintaining atmospheric pressure therein suitable toprevent an induced air flow through 17 but receptive to admit vaporsfrom conduits 18 and 19.

To purge the canister of collected vapors, passage B is placed incommunication with a vacuum obtained at location 10 in the intakemanifold immediately below the throttle of the carburetor (this locationis commonly referred to as the PCV port). The passage B is maintainedclosed when purging is not desired by the first control means E. Means Ecomprises a valve housing 26 having a boring or channel 22, one end 22aof the channel serving as the inlet for vacuum; a cross bore 21intersects with boring 22. Passage B is interrupted by means E so thatone break in passage B becomes the inlet at 22a and the other break inpassage B becomes the outlet for the vacuum through crossbore 21. Avalve 24 (urged by spring 29) is adapted to normally close off theconnection between bore 21 and boring 22 by seating against surface 27.Valve 24 is attached to a diaphragm 28 residing in chamber 23; thediaphragm is actuated by a vacuum signal in conduit 25. The vacuumsignal is taken at location 9 (commonly referred was the spark port)and'the vacuum here is relatively non-existentat idle or wide-'open-.

ing, control means F is employed to vary the aperture of passage B.Means-F comprises a'valve housing 30 defining an interior valve seat 31which is progressively closed, but never completely, by a spring biasedvalve element 32 acting in response to intake manifold vacuum in passageB thereby to vary the spacing between element 32 and the seat 31. MeansF functions to allow more flow through, the lower the vacuum pressure;the latter vacuum force purges the vapors and acts proportionate toengine loading. There is a slight bleed through means F even in its mostrestricted position when vacuum pressure is the highest. Thus, theflowis not preprogrammed independent of engine operation.

We claim: i 1. In an internal combustion engine having a fuel system, anintake manifold and a carburetor with a throttle to provide a gaseousmixture engine flow, an apparatus for controlling the recovery of fuelvapors in said system, comprising: i

'a. means for-adsorbing and storing said fuel vapors, b. a passage forpurging said stored fuel vapors and for conveying said vapors to saidintake manifold, c. a first control means responsive to vacuum upstreamfrom said throttle for maintaining said pas- 4 sage in either afullyopen'ed or a fully closed condition, said passage having internalwalls defining an aperture between said first control means and saidmeans, for absorbing vapors and through which flow must pass in saidpassage, and d. a second control means responsive to vacuum in l saidintake manifold for regulating the aperture of said passage whereby'said storing-means is desorbed at a rate inversely proportional toengine flow.

2. An apparatus as in claim 1, in which said second 4. The apparatus asin claim 1, which further comprises, in combination with' saidapparatus, an engine exhaust system having a catalytic converter andmeans calibrated to vary in response to predetermined air/fuel mixtures,said second control means being effective to regulate desorption of'fuel vapors from said storing means in such amounts as to maintainsaidcalibrated means in a condition to provide an air/fuel mixture at 'leastabove 14/1 whereby the amount'of carbon monoxide in said exhaust gassystem is maintained in a predetermined range compatible for operationof said catalytic converter 1 i

1. In an internal combustion engine having a fuel system, an intakemanifold and a carburetor with a throttle to provide a gaseous mixtureengine flow, an apparatus for controlling the recovery of fuel vapors insaid system, comprising: a. means for adsorbing and storing said fuelvapors, b. a passage for purging said stored fuel vapors and forconveying said vapors to said intake manifold, c. a first control meansresponsive to vacuum upstream from said throttle for maintaining saidpassage in either a fully opened or a fully closed condition, saidpassage having internal walls defining an aperture between said firstcontrol means and said means for absorbing vapors and through which flowmust pass in said passage, and d. a second control means responsive tovacuum in said intake manifold for regulating the aperture of saidpassage whereby said storing means is desorbed at a rate inverselyproportional to engine flow.
 2. An apparatus as in claim 1, in whichsaid second control means comprises a valve biased to a minimum aperturecondition and progressively opened in opposition to said bias by anincrease in intake manifold vacuum.
 3. An apparatus as in claim 2, inwhich said second means is actuated in response to PCV port vacuum. 4.The apparatus as in claim 1, which further comprises, in combinationwith said apparatus, an engine exhaust system having a catalyticconverter and means calibrated to vary in response to predeterminedair/fuel mixtures, said second control means being effective to regulatedesorption of fuel vapors from said storing means in such amounts as tomaintain said calibrated means in a condition to provide an air/fuelmixture at least above 14/1 whereby the amount of carbon monoxide insaid exhaust gas system is maintained in a predetermined rangecompatible for operation of said catalytic converter.